Mechanical,flow and electrical properties of thermoplastic polyurethane/fullerene composites: Effect of surface modification of fullerene

Thermoplastic polyurethane (TPU) composites with fullerene loadings varying from 0.5 to 2 weight% were prepared by melt-mixing method. Nitric acid oxidation and silanization were applied to fullerene surface to improve interfacial interactions with TPU matrix. The influence of surface modifications of fullerene on mechanical, melt flow and electrical properties of TPU based composites were investigated. Incorporation of fullerene leads to nearly twofold increase in tensile strength and Young's modulus of the composites in addition to enhancing the flexibility. The best results are obtained in nitric acid and silane modified fullerene containing composites at the lowest concentration (0.5%). Higher MFI values were observed for composites loaded with surface treated fullerenes compared to pristine fullerene because of their better dispersion in TPU. Electrical properties of TPU also improved by the addition of surface modified fullerene particles. Surface oxidation and silanization gave rise to dispersion homogeneity which may be the reason of both tensile strength and strain improvements at the same time.     

Processing parameters and characterisation of flax fibre reinforced engineering plastic composites with flame retardant fillers

This work studies the possibility of compounding natural fibres (flax) into engineering plastics (PA6 and PB6) and comparing the results with counterpart glass fibre composites. The problem in compounding is the difficulty to compound the fibres with such polymers of high melting temperatures without decomposing the natural fibre thermally. Preliminary experiments are tried to define the possible processing window using the kneader namely temperature, compounding time and shear rate. Fibre content is tried in range of 0–50 wt.% with 10% step. The mixing temperature covers the range around the melting temperature ‘Tm’ [Tm−20, Tm+20]°C. The use of pre-melting temperature in compounding would utilise the energy evolving by fibres mutual rubbing. Compounding time is optimised at the minimum level. Shearing rate is tried at 25, 50, 75 and 100 rpm. Optimum conditions are defined to be 210–230 °C and 200–210 °C for PBT and PA6 respectively. Shearing rate is also defined to lie within 25–50 rpm.Two different additives of non-organic mineral and organic phosphate flame retardants are tried with the prepared composites either alone or in combination with each other. The loading of flame retardants is limited to 20 wt.% in order to leave a space for natural fibres as well as the polymer and to keep in turn the overall composite mechanical properties. A mix of 1:1 ratio between the both types of retardants is needed to reach V0 flame retardation level. Mechanical properties are even improved 30% in E-modulus and 4% in strength with respect to composites without flame retardants. However, the injection moulding is reported to be difficult because of the high viscosity and the parameters should be optimised regarding the desired flame retardance level and the required mechanical properties as well as keeping the fibres not damaged.     

Effect of coupling agent on natural fibre in natural fibre/polypropylene composites on mechanical and thermal behaviour

To enhance the adhesion between the natural fibre and the thermoplastic matrix, a coupling agent of maleic anhydride grafted polypropylene MAPP is applied. In literature, there are different guidelines of the optimum percentage required of MAPP. Therefore, a systematic work is carried out to optimise the MAPP percent with respect to the type of the natural fibre. Different parameters are investigated namely; Coupling agent ratio to the fibre (0%, 6.67%, 10%, 13.3%, 16.67%), coupling agent source, fibre type (flax, hemp, sisal), and fibre content (30%, 50%). Composite is produced using a kneader and the resulting material is assessed mechanically, thermally, microscopically and for water absorption. For different MAPP source and the natural fibre type, optimum MAPP to fibre ratio is found in average to range between 10% and 13.3% according to the investigated property (stiffness, strength and impact). Increase of MAPP is found to decrease the melting temperature. The thermal behaviour is also linked to the copolymer molecular weight.     

Influence of an Agatha flax fibre location in a stem on its mechanical,chemical and morphological properties

The mechanical properties of flax fibres are analysed as a function of their biochemical and morphological characteristics. The fibres, from the Agatha variety, have been selected from either the top, the middle or the bottom of the stems. The results of each analysis are discussed according to the position of the fibre in the stem and compared among themselves. Considering a flax fibre as a natural composite, this study underlines the complexity of its structure and shows that many parameters intervene in its deformation behaviour.     

Mechanical behavior of Kevlar/basalt reinforced polypropylene composites

In this study, mechanical behavior of thermoplastic composites reinforced with two-dimensional plain woven homogeneous and hybrid fabrics of Kevlar/basalt yarns was studied. Five types (two homogeneous and three hybrids) of composite laminates were manufactured using compression molding technique with polypropylene (PP) resin. Static tensile and in-plane compression tests were carried out to evaluate the mechanical properties of the laminates. The tension and in-plane compression tests had shown that the composites with the combination of Kevlar and basalt yarns present better tensile and in-plane compressive behavior as compared to their base composites. Improvement in the properties such as elastic modulus, strength and failure strain in both tension and in-plane compression was observed due to the hybridization. Numerical simulations were performed in ABAQUS/Standard by implementing a user-defined material subroutine (VUMAT) based on Chang-Chang criteria. Good agreement between the experimental and numerical simulations was achieved in terms of damage patterns.     

The effect of reprocessing on the mechanical properties of polypropylene reinforced with wood pulp,flax or glass fibre

Composites of polypropylene, substitutable for a given application and reinforced with: Medium Density Fibreboard fibre (MDF) (40 wt%); flax (30 wt%); and glass fibre (20 wt%), were evaluated after 6 injection moulding and extrusion reprocessing cycles. Of the range of tensile, flexural and impact properties examined, MDF composites showed the best mean property retention after reprocessing (87%) compared to flax (72%) and glass (59%). After 1 reprocessing cycle the glass composite had higher tensile strength (56.2 MPa) compared to the MDF composite (44.4) but after 6 cycles the MDF was stronger (35.0 compared to 29.6 MPa for the glass composite). Property reductions were attributed to reduced fibre length. MDF fibres showed the lowest reduction in fibre length between 1 and 6 cycles (39%), compared to glass (51%) and flax (62%). Flax fibres showed greater increases in damage (cell wall dislocations) with reprocessing than was shown by MDF fibres.     

Mechanical properties and toughening mechanisms of polypropylene/barium sulfate composites

The effect of interfacial interaction on the mechanical performance of a group of polypropylene (PP)/barium sulfate (BaSO₄) composites were studied. It was found that PP can be toughened with specially treated BaSO₄ particles. The interfacial modification contributes to the toughening in two aspects. The first is to provide a proper interfacial adhesion and control the interfacial debonding occurs at well-timed stages. This ensures the inorganic particles transfer the stress and stabilizes the cracks at the initial stage of the deformation, and satisfy the stress conditions for plastic deformation of matrix ligaments subsequently via debonding. The second is that the modified interface between PP matrix and filler particles increases the nucleating ability of the fillers and retards the motion of the PP chains. This leads to the formation of PP crystals with less perfection and smaller size in the matrix and promotes plastic deformation of the matrix after the debonding occurs.     

Influence of refiner fibre quality and fibre modification treatments on properties of injection-moulded beech wood–plastic composites

Thermo-mechanical pulp (TMP) fibres made from beech wood were produced using increasing refiner gap widths and thus with increasing fibre length and coarseness. Fibres (60% by weight) were compounded in an internal kneading mixer using high-density polyethylene as the matrix and injection-moulded. Fibre lengths and length/width ratios were determined (a) before processing and (b) after injection-moulding and Soxhlet extraction using the optical FibreShape system. An increase in fibre length resulted in a decrease in water absorption and an improvement in flexural strength and modulus of elasticity of the wood–plastic composites (WPC). However, flexural strength of the WPC with TMP fibres was not improved compared to WPC with wood flour when maleic anhydride-grafted polyethylene (MAPE) was used as a coupling agent. After injection-moulding, differences in length of the various TMP fibre types were minor. Fibre geometry before processing strongly influences the water absorption and flexural properties of the composite. Fibre treatment with emulsified methylene diphenyl diisocyanate (EMDI) resin before compounding was shown to be equally efficient in reducing water absorption and improving flexural strength as the addition of MAPE during the compounding step.     

Highly aligned flax/polypropylene nonwoven preforms for thermoplastic composites

A major challenge for natural fibre composites is to achieve high mechanical performance at a competitive price. Composites constructed from unidirectional yarns and woven fabrics are known to perform significantly better than composites made from random nonwoven mats, but unidirectional yarns and fabrics are much more expensive to manufacture than random nonwoven mats. Here, we report on highly aligned natural fibre nonwoven mats that can be used as a replacement for unidirectional woven fabrics. A drawing operation is added to the conventional nonwoven process to improve fibre alignment in the nonwoven preforms and the final composites. The modified nonwoven manufacturing process is much simpler and cheaper than the unidirectional woven fabric process because of the elimination of expensive spinning and weaving operations. The composites fabricated from the highly aligned nonwoven mats showed similar mechanical strength as the composites made from unidirectional woven fabrics.     

Polypropylene/natural fibres composites: Analysis of fibre dimensions after compounding and observations of fibre rupture by rheo-optics

Fibre size distribution and the way how fibres are breaking during compounding with polypropylene were analysed. Two types of cellulose-based fibres were used: natural flax and man-made (regenerated) cellulose, Tencel. No significant influence of Tencel initial fibre size on its final size after processing was observed. However, the fibre type and the presence of defects have a stronger effect on the rupture. The value of the average final length of flax fibres was found to be similar to the distance between kink bands.In order to understand fibre rupture mechanisms, they were observed using a rheo-optical system which enabled visualization of fibre break-up. All fibres studied broke by fatigue after an accumulation of strain, contrarily to what is known for glass fibres. Flax fibres broke around the kink bands while Tencel® broke after numerous bending.     

Pairing effect and tensile properties of laminated high-performance hybrid composites prepared using carbon/glass and carbon/aramid fibers

Many attempts have been made to fabricate lightweight, high-performance, and low-cost polymeric composites. To improve the mechanical performance of the same material compared to conventional composites, paired hybrid materials were manufactured with different lamination structures. Each of six types of hybrid composite was designed by lamination pairing of carbon/aramid fabric and carbon/glass fabric using VARTM. The dependence of the mechanical properties of the samples on the pairing effects of the lamination structures was investigated. All pairing materials did not lead to a large increase of tensile strength due to the domination of carbon fiber, but the mechanical properties of specific laminates were clearly changed by the particular pairing sequence used. Using the limited material, the design of an effective structure was the central laminating condition with a good tensile and bending properties. Laminating position of the carbon fiber was found to play an important role in the stacking design of hybrid composites.     

Procedural influences on compression and injection moulded cellulose fibre-reinforced polylactide (PLA) composites: Influence of fibre loading,fibre length,fibre orientation and voids

The influence of fibre loading (20, 30, 40 mass%), fibre fineness, and the processing procedure (compression moulding – CM and injection moulding – IM) on the tensile and impact strength of lyocell/PLA composites was examined. The results revealed a significantly higher tensile and impact strength for CM composites compared to IM composites. An increase in strength up to a fibre loading of 40% was determined for CM composites, while for IM composites the highest values were measured at a fibre loading of 30%. Composites were investigated for their void content, fibre orientation, fibre length and process-induced fibre damage. A better fibre/matrix adhesion and compaction of IM composites was found while fibre orientation as well as mechanical properties of extracted fibres show no significant differences between CM and IM composites. The different mechanical characteristics of CM and IM samples are attributed predominantly to the fibre aspect ratio and the distribution of voids.     

Damage to flax fibre slivers under monotonic uniaxial tensile loading

Usual testing methods developed for synthetic fibre bundles or slivers do not suit for plant fibres which exhibit specific characteristics. This paper reports damage investigation in flax fibre slivers (collection of disentangled and aligned fibre bundles more or less bonded by bark residues or other tissues) especially prepared for uniaxial tension testing using a new methodology and a dedicated device.The analysis of the acoustic emission data by using clustering methodology allowed categorizing three populations of damage mechanisms. Identification of the damage mechanisms was made by correlation of the tensile loading curves with acoustic emission data and by optical observations. Different damage parameters defined from the mechanical data (released elastic energy) were compared with those from acoustic data (energy of the hits). The results showed that the extension of damage vs. deformation can be expressed by using either of these two data sets.     

Mechanical properties of fire-retardant glass fiber-reinforced polymer materials with alumina tri-hydrate filler

Alumina tri-hydrate (ATH) can be effectively used to increase fire resistance of Fiber-Reinforced Polymer (FRP) materials. This paper studies the effect of ATH filler on mechanical properties of Glass FRP (GFRP) material, based on compression, tension, shear and flexural test results from three types of GFRP materials with the amount of 0% (control), 25%, and 50% ATH filler by weight of the resin. It was found that the control was the strongest for all tests except for flexure, which is 3% lower than the flexural strength of 25% ATH sample. The compressive strength dropped 19% and 25% for 25% and 50% ATH loadings, respectively, compared to the control. For shear and tensile strengths, the 25% ATH sample acted similarly to the control, but the 50% ATH sample had a significantly lower strength. For stiffness, changing the additive amount from 0% to 50% had only small changes for compression, tension, and flexure. It can be concluded that adding ATH generally decreases the strength and makes FRP more brittle. The performance of a 25% ATH loading is comparable to the control except compression, while a 50% ATH loading has a more significant effect on the mechanical properties of the GFRP. The data presented in this paper can be used to develop fire-resistant FRP systems.     

Mechanical reinforcement while remaining electrical insulation of glass fibre/polymer composites using core–shell CNT@SiO2 hybrids as fillers

Carbon nanotubes (CNTs) have been widely used as mechanical reinforcement agents of composites. However, their aggregations, weak interfacial interaction with polymer, as well as high electrical conductivity limit their use in some especial applications. In this paper, the silicon oxide (SiO₂)-coated (CNT@SiO₂) core–shell hybrids with different SiO₂ thickness were prepared and employed to reinforce glass fibre-reinforced bismaleimide–triazine (BT) resin (GFRBT) composites. The results indicated the mechanical properties, including tensile strength and Young’s modulus increased with the increase of SiO₂ thickness and CNT@SiO₂ loading. Such enhanced mechanical properties were mainly attributed to the intrinsically nature of CNTs, homogeneous dispersion of the hybrids, as well as improved interfacial interaction. Meanwhile, the composites remained high electrical insulation (9.63 × 10¹² Ω cm) due to the existence of SiO₂ layer on CNT surface. This study will guide the design of functionalized CNTs and the construction of high-performance composites.     

Thermomechanical properties of bio-based composites made from a lactic acid thermoset resin and flax and flax/basalt fibre reinforcements

Low viscosity thermoset bio-based resin was synthesised from lactic acid, allyl alcohol and pentaerythritol. The resin was impregnated into cellulosic fibre reinforcement from flax and basalt and then compression moulded at elevated temperature to produce thermoset composites. The mechanical properties of composites were characterised by flexural, tensile and Charpy impact testing whereas the thermal properties were analysed by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The results showed a decrease in mechanical properties with increase in fibre load after 40 wt.% for the neat flax composite due to insufficient fibre wetting and an increase in mechanical properties with increase fibre load up to 60 wt.% for the flax/basalt composite. The results of the ageing test showed that the mechanical properties of the composites deteriorate with ageing; however, the flax/basalt composite had better mechanical properties after ageing than the flax composite before ageing.     

Effect of material and process parameters on the mechanical properties of unidirectional and multidirectional flax/polypropylene composites

Unidirectional (UD) and multidirectional (MD) flax/polypropylene composites were studied. Flax with varying retting degree and boiled flax was used as reinforcement for the UD composites and unmodified and maleic acid anhydride modified polypropylene (MAA-PP) was used as matrix. Multidirectional flax/polypropylene composites were manufactured on laboratory scale and on pilot scale. They were made from needle-punched hybrid flax/PP non-wovens. Normally retted flax as well as boiled flax was used. For the specimens made on pilot scale, a third kind of flax, namely bleached flax was also studied. The influence of different process times and temperatures on the mechanical properties of the composites was analysed. Generally, the composites have adequate good mechanical properties. The unidirectional composites of boiled flax combined with MAA-PP show the best mechanical properties. Contrary to the UD composites, flax treatment did not lead to the expected property improvements for MD composites.     

Microstructure,flexural properties and durability of coir fibre reinforced concrete beams externally strengthened with flax FRP composites

This study investigated the flexural behaviour of plain concrete (PC) and coir fibre reinforced concrete (CFRC) beams externally strengthened by flax fabric reinforced epoxy polymer (FFRP) composites. PC and CFRC beams without and with FFRP (i.e. 2, 4 and 6 layers) reinforcement were tested under three- and four-point bending. The microstructures of coir fibre, coir/cement matrix, flax/epoxy matrix, and FFRP/concrete interfaces were analysed using scanning electronic microscope (SEM). Test results indicated that the peak load, flexural strength, deflection and fracture energy of both PC and CFRC specimens enhanced proportional to an increase of FFRP layers. Coir further increased load, strength and energy of the specimens remarkably. It was also found that the thickness and coir influenced the failure modes while the test method influenced the load and energy of the specimens remarkably. SEM studies showed effective bond at coir/cement, flax/epoxy and FFRP/concrete interfaces. Therefore, it concluded that natural FFRP composites can be used to repair or retrofit existing concrete structures.     

A comparative study of fatigue behaviour of flax/epoxy and glass/epoxy composites

Experimental investigations on flax and glass fabrics reinforced epoxy specimens, i.e. FFRE and GFRE, submitted to fatigue tests are presented in this paper. Samples having [0/90]_3S and [±45]_3S stacking sequences, with similar fibre volume fractions have been tested under tension–tension fatigue loading. The specific stress-number of cycles to failure (S–N) curves, show that for the [0/90]_3S specimens, FFRE have lower fatigue endurance than GFRE, but the [±45]_3S FFRE specimens offer better specific fatigue endurance than similar GFRE, in the studied life range (<2 × 10⁶). Overall, the three-stage stiffness degradation is observed in all cases except for [0/90]_3S FFRE specimens, which present a stiffening phenomenon of around 2–3% which could be related to the straightening of the microfibrils.     

Environmental advantage by choice: Ex-ante LCA for a new Kraft pulp fibre reinforced polypropylene composite in comparison to reference materials

This study analyses the circumstances of environmental advantage by benchmarking a novel Kraft pulp fibre reinforced polypropylene against its matrix material and two other composites with talcum and glass fibres. With one exception, all composites use less non-renewable energy (−1% to −29%), but only the Kraft pulp fibre reinforced polypropylene achieves a reduction in global warming potential (14% to 35%) considering different functional units compared to polypropylene. The comparisons on basis of function–strength and stiffness in this case study–show that the adequate application of specific material properties, are key to achieve environmental advantages.